In general, in a film for packaging various hydrous foods typified by meat, processed meat foods such as sausage, fresh vegetables and seafood, and other processed foods, food is hardly visible due to fogging caused by water vapor that is vaporized from the food, adheres to and condenses on the inner surface of the film. Thus, the film is required to have antifogging properties to prevent fogging.
In order to exhibit antifogging properties, there are proposed methods for imparting antifogging properties by adding a surfactant to a film of the innermost surface layer as an antifogging agent to improve wettability of the surface (for example, Patent Documents 1 to 3). However, in this method, when a large amount of surfactant is used, there is a concern of bleed-out occurring over the surface of the film.
Another known method for imparting antifogging properties is a method of imparting wettability by performing a corona treatment on the surface of a film. However, in the case of performing a corona treatment, the strength of a heat-sealed portion may be decreased by the treatment. In order to prevent the strength from being decreased, for example, a method of selectively performing a corona treatment on only portions other than the sealed portion is proposed (for example, Patent Document 4). However, the method of performing a corona treatment on only a specific region of the surface of the film has complicated the operations and the number of steps increases. Thus, there has been a demand for establishing an industrially advantageous method.